And answering when was silver first used as currency is complicated. For thousands of years, we have traded with and for precious metals. It will be no surprise that the first cases of trading for silver are difficult to discern.
Moreover, when did silver stop being traded as barter, and become a monetary unit? The Code of Hammurabi shows trade based in intangible credits and debits, as well as cash-like transactions, but makes scarce mention of which came first.
According to Samuel N. Kramer's History Begins at Sumer the Ancient Mesopotamians developed commodity currencies in the bronze age. You can argue that first time silver was used as a currency would be around 3000 BC. But does that really answer when was silver first used as currency? You could also argue no. In fact, there is evidence that the ancient Egyptians used gold bars as well as silver as reference points to standardize trade.
What you really want to know is when people began cutting up the metal and using it as true standard currency for the masse. To do that we need to go to early Ancient Greece. In those days, the largest empires were hardly larger than present day Greece. As the society progressed, there was increasingly a need for a single currency with the same value over a large land mass.
Only later, with the Roman Empire did societies see a truly standardized value of coinage across the Empire. Through repeated creative destruction rise of money had a profound and civilizing effect on humanity. But for these events, others in the history of silver, such as the Spanish conquest of South American, and the flooding of European markets would never have happened.
The origins of coinage are complex, and at many points tied directly to silver. The Lydian trite was made of electrum (a gold and silver alloy). The coin weighed just under 5 grams and is argued to be the oldest coin in the world. This multifarious alloy became the most important signifier of value in Greece over 4,000 years ago.
By the Greek's and later the Persian's spreading the Lydian tradition, money began to take shape around the world. Moreover, this began the silver ingot's global circulation as a bartering system.
Silver's popularity grew during the many years of the Athenian Empire, when the current capital of Greece asserted economic and cultural dominance over other cities states and beyond. The silver ‘Tetradrachm’ was so popular that it achieved the “International standard” as a coin throughout the Mediterranean. Still, is there something more in the history books for us?
Silver's renowned status traces back a long way. Internationally, Chinese Spade Currency from the Zhou Dynasty came about from the 6th century BC to the middle of the 5th century BC. The drachma, one of the world's earliest silver coins, dates to 6th-century BC. It represents a clear historical landmark for when the barter system transitioned into hard currency.
The Athenians, ever the active traders in Greece and beyond, stretched their influence into modern-day Macedonia, Turkey, and North Africa. Some of thier ancient coins can still be found if you have the pleasure of going hunting for junk silver in Athens!
So during these nascent years of economic growth via trade it was silver that had the most value. In fact, despite engaging in plenty of wars and trade with the Greeks, the Persians knew little about coinage until the middle of the 5th century BC.
Seeing the trade value, they quickly began to produce it themselves. Persian accounts of the time make it clear that gold appeared alongside silver in coinage but silver was still the predominantly sought-after due to Greek trade.
A few hundreds years after the Greeks, a larger network of currency evaluations was set up. It took an Empire as expansive as the Romans to institute the first currency with values that held firmly beyond borders. Roman currency was a mixture of gold, silver, bronze, orichalcum and copper pieces. Moving beyond it's predecessors, this fact made it currency in the very modern sense.
Still, the Roman influence on modern day coinage is seen evidently in the term ‘mintage.’ The word comes from the manufacture of silver coins in 269 BCE at the Juno Moneta Temple in Rome. Moneta was a Roman goddess in the constellation of pagan spirits that ruled the world. Her spirit was deemed to have flowed into the silver coins manufactured at her temple.
A fun fact to conclude with is that the English word ‘mint’ is actually derived from the Latin word Moneta. Keep in mind a closer companion seems to be the word ‘money!’
The ancient lineage of silver is part of the reason why it has such value today. Though it’s spot price has remained at an affordable rate over recent years, the value of silver will always be more than the paper money you use to buy it with.